Conventional throttle control apparatus are disclosed in Japanese Patent Laid-open Print Nos. 58(1983)-155255 and 61(1986)-89940. In these conventional apparatus, an electric controller is associated with an accelerator operation mechanism and the amount of operation thereof is fed to the controller. From the controller, the resultant operational amount, as a signal, is fed to a motor for adjusting an opening of a throttle valve. The throttle valve is urged toward its fully closed condition by a return spring. Thus, the motor driving for adjusting the opening of the throttle valve is established against the urging force of the return spring.
However, in the conventional throttle control apparatus, when an electric failure occurs, the function of the motor ceases, resulting in the throttle valve being brought into its fully closed condition. Thus, an engine stall will occur while the engine runs, or an ignition of the engine cannot be established when the engine is about to be initiated.